Operation and maintenance of cathodic protection system

1、 Preparation and acceptance of cathodic protection before putting into operation

Before cathodic protection is put into operation, the pipeline to be protected shall be inspected. If there is no insulation, there is no protection. Before applying cathodic protection current, it is necessary to ensure that all insulation measures of the pipeline are correct. There should be no leakage points on the surface of the pipeline, and the protected pipeline should have continuous conductivity.


2、 Daily maintenance and management of Cathodic Protection Station

Check the electrical equipment circuit connection firmness, the correctness of installation, electrical components whether there are mechanical obstacles. Check whether the fuse of the fuse on the distribution board is properly connected according to the regulations. Observe the electrical instrument, record the output current and electrified potential value on the special form, and check whether there is any change compared with the previous record. Regularly check the working grounding and arrester grounding, and ensure that the grounding resistance is not greater than 10 ohm. Do a good job in cleaning and sanitation of the equipment in the station, pay attention to keep the indoor dry, well electrified, do a good job of ventilation, and prevent the instrument from overheating.


3、 Maintenance of sacrificial anode

   1. The daily maintenance work of pipeline sacrificial anode protection is not much. In addition to the protection potential measurement, test pile maintenance, insulation joint detection, grounding fault removal and other work according to the requirements of impressed current cathodic protection, it is recommended to measure the parameters every year. According to this, the pipeline protection situation is analyzed. If the performance of the prototype deteriorates, corresponding measures should be taken.


   2. During the annual inspection, the output current of sacrificial anode can be measured to repair the broken cable.

   3. If the output current of anode decreases obviously and the anode does not reach its life, the short circuit of anode cable is the common reason. The ammeter can be connected in series in the anode cable to measure the anode output current, or a resistance of 0.1 Ω can be connected in series in the anode cable. The anode current output can be calculated by measuring the voltage drop on the resistance.

   4. The grounding resistance of anode is anode open circuit potential minus anode closed circuit potential divided by anode output current.


4、 Analysis of common faults in cathodic protection system

   1. The harm of poor pipeline insulation and leakage fault
After the cathodic protection station is put into operation or the sacrificial anode protection is put into operation for a period of time, the phenomenon that the output current of the sacrificial anode group increases while the pipeline protection distance is shortened under the specified power on point; or in the sacrificial anode system, the output current of the sacrificial anode group increases, and its value has exceeded the protection current demand of the pipeline, but the protection point still fails to reach the specified index 。 It is called imprint to protect pipeline leakage.

   2. Causes of electric leakage
Improper construction, insulation joint failure or leakage, metal sleeve crossing, pipeline and grounding grid short circuit.

   3. How to judge the short circuit between pipeline and grounding grid

To judge whether there is a short circuit between the grounding electrode and the pipeline, the method of potential measurement can be used. The reference electrode is used to measure the potential of pipeline and grounding electrode respectively. The potential of short circuit grounding electrode and pipeline is the same. Or measure the potential difference between the grounding electrode and the pipeline. If the potential between the two is zero, it can be judged that there is a short circuit between the grounding grid and the pipeline.

   4. Search for leakage point of anticorrosive coating
The method of using DCVG to find the damaged point of anticorrosive coating of pipeline and determine the leakage point or short contact point of pipeline. This method first sends the pulse signal to the pipeline to be tested. If the pipeline coating is good, the current flowing into the pipeline is very weak, and the instrument does not display it. If the anticorrosive coating of the pipeline is damaged, the current will leak into the pipeline through the damaged place from the soil, and the current flow will produce obvious potential gradient in the surrounding soil. When the detector holds two reference electrodes to detect and walk directly above the pipeline, the voltmeter will vibrate. When the pointer of the voltmeter stops shaking, the middle of the two reference electrodes is the leakage point of the anticorrosive coating.

   5. Near distance potential measurement along the pipeline
It is usually used to check the working condition of cathodic protection system by measuring the point position on the test pile. In this way, even if there is a leakage point in the pipeline coating, if the leakage point is far away from the test pile, it is difficult to detect it through the potential measurement of the test pile. Therefore, the closer the potential measurement is, the more tender the measurement result will be, which will reflect the actual situation of cathodic protection of pipelines. In order to eliminate the IR drop, a short circuit is installed in the cathodic protection circuit, and all the power supplies connected to the detected pipeline should be turned on and off at the same time, so as to measure the on-off potential of the bag pipe.

   6. Aging test of pipeline anti-corrosion coating
Electromagnetic method can reflect the general condition of anticorrosive coating, buried depth of pipeline and defect location of coating. Its principle is to input a voltage signal to the pipeline, and the detector detects the attenuation degree of the signal along the pipeline. When there is a sudden attenuation of the coating on the pipeline, it shows that the signal attenuation is smooth.

   7. The safety of maintenance type in cathodic protection system
On the way to the construction site, you should pay attention to safety, whether by bus, by boat or by plane. When surveying in the field, pay attention to the attack of poisonous snakes and beasts. When working on the rectifier, disconnecting the switch on the panel does not mean that it is safe to operate inside the equipment. AC power should be disconnected and safety locks and labels should be installed. Before contacting the rectifier, check whether the shell is charged with electric pen.